1. Field of the Invention
The present invention relates to a MEMS (Micro Electro-Mechanical System) device package and a method of manufacturing the same.
2. Description of the Related Art
The field of MEMS is a technical field for processing sensors, micro-actuators, gyroscopes, or parts for precise machines using a semiconductor processing technique. Therefore, the use of MEMS is considered as a technique for improving performance and reducing costs as the precise workability, uniformity between products, superior productivity, etc., of the semiconductor technique can be applied to MEMS.
MEMS devices, for example, accelerometers, angular velocity sensors, resonance type gyroscopes, etc. are packaged for the purpose of enhancing protection and/or sensitivity thereof. As high densification and miniaturization of MEMS devices are realized due to the rapid development of techniques for manufacturing MEMS devices, it is also required to miniaturize packages of the MEMS devices. For this purpose, a WSP (Wafer Scale Package) technique is frequently attempted, which performs packaging of devices while the devices are in a wafer condition.
FIG. 1 is a cross-sectional view schematically showing an example of a conventional MEMS device package. As shown in the drawing, a device substrate is provided with a MEMS active device 2, and a covering glass substrate 3 is joined to the device substrate 1 for protecting the MEMS active device 2. The MEMS active device 2 generally comprises a spring structure and a stage supported by the spring structure.
In addition, inner electrode pads 4 are provided on the opposite side portions of the device substrate 1, in which the inner electrode pads are electrically connected with the MEMS active device 2. Furthermore, a trench 5 is formed in the covering glass substrate 3 to provide a space in which the MEMS active device 2 is positioned, and the covering glass substrate 3 and the device substrate are anodic-bonded to one another.
Furthermore, via holes 6 are formed through the opposite side portions of the covering glass substrate 3 and outer electrode pads 7 are formed through the via holes 6, in which the outer electrode pads 7 are connected with the inner electrode pads 4. Here, the outer electrode pads 7 are formed by filling metal (typically, aluminum (Al)) in the via holes 6 through a sputtering process. The outer electrode pads 7 are each connected with a signal line on a circuit board (not shown) via a wire, a bump or the like.
In the above-mentioned conventional MEMS device package, there is no way to avoid the increase in thickness of the covering glass substrate 3 because a structure and a manufacturing process that the glass-based covering substrate 3 and the silicon-based device substrate 1 are bonded to one another through anodic-bonding are adopted. In addition, there is a limit in reducing the size of the package because the via holes 3 are formed through the glass substrate 3. Consequently, the above-mentioned conventional package contributes to an obstruction in miniaturizing an appliance which employs such a MEMS package, because it is high and large in size and thus occupies a large volume in the appliance.
Furthermore, by employing the glass-based covering substrate 3, the above-mentioned conventional MEMS device package has a problem in that the processes for forming the via holes 6 for electrode-wiring and the outer electrode pads 7 are very complicated and require a lot of time, thereby causing a drop in yield and productivity. The conventional MEMS package also has a problem in that the MEMS active device 2 may be deformed or damaged due to high temperature at the time of anodic-bonding (typically, about 460° C.) and inherent stress is included due to the difference in thermal expansion coefficient between the covering glass substrate 3 and the device substrate 1.
In addition, the circuit connection between the inner electrode pads 4 formed from silicon and the outer electrode pads 7 formed from a metallic material such as aluminum (Al) may present a problem in terms of reliability of the device because such a circuit connection generates very high inductance in connection with the electric contact resistance at the contact areas and RF of high frequency, thereby causing a great signal loss.
Meanwhile, existing bonding materials such as SnPb are spread out laterally when bonding a wafer and a glass material, whereby uniformity may be deteriorated or poor quality may be frequently caused in forming a rim of the package.